1. Field of the Invention
This invention relates to vapor growth of semiconductor and more particularly to monitored vapor growth of doped semiconductor.
2. Description of the Prior Art
Vapor growth techniques play a very important role in processing of semiconductor devices. Epitaxial vapor growth of a high resistivity layer on a low resistivity substrate enabled the recent high speed integrated circuits. With the progress of the designing of semiconductor devices, there is an intense demand for precisely controlling the doping profile. Most of the epitaxial growth, however, is controlled only empirically through the mixing ratio of dopant and the growth temperature. These parameters are usually kept constant during growth. Impurities in a semiconductor body are subjected to solid diffusion or redistribution in any high temperature process. Accordingly, when an epitaxial layer of a high resistivity (low net impurity concentration) is grown on a substrate of a low resistivity (high net impurity concentration), the epitaxial layer is subjected to impurity diffusion from the substrate. Similar impurity diffusion occurs between any adjacent semiconductor regions.
Recently, monitoring of epitaxial growth, especially in-situ monitoring, is attracting attention. On-line monitoring was proposed in Japanese Patent Publication No. 44787/1978, in which the doping gas was sampled from the path of the doping gas before mixing with the carrier gas for controlling the impurity concentration in the doping gas. The doping gas is analized through flame spectroscopy. Provision of a sampling capillary in a reaction chamber was also proposed for the in-situ monitoring and controlling of epitaxial growth, in Japanese Utility Model Laid-Open Publication No. 62070/1977.
Epitaxial growth has an advantage that the doping level can be widely varied in time during a single growth process without intervening any other process. For example, when an epitaxial layer of a low impurity concentration is to be grown on a substrate including a semiconductor region of high impurity concentration, there may be successively formed on the substrate initially a thin layer of a relatively high doping level for compensating the impurities redistributed from the region of high impurity concentration and then the main epitaxial layer of the predetermined low doping level. Such a counterdoping technique is widely known, but can modify the doping profile only in limited manner and to limited accuracy. It is apparent that epitaxial growth can potentially provide various doping profiles as desired, but to the inventors' knowledge there is no proposal for the control of doping profile in very wide variations, more particularly no proposal for the computer-aided design and in-situ control of the doping profile in a semiconductor wafer.